The present invention relates to an a method for producing impeller for turbine pumps provided with vanes having an improved profile.
In particular, the impeller produced by the method according to the present invention is of the monolithic type obtained by casting a metal in a die. It is known that turbine pumps convert the mechanical energy that they receive from a motor into pressure energy of a fluid.
The basic part of the turbine pump is the impeller, which transfers the total energy to the unit of mass of the fluid that flows through it, partly as pressure energy and partly as kinetic energy.
The impeller of a turbine pump is substantially constituted by two elements which are substantially disk-shaped and between which the vanes are arranged; the vanes convey the fluid, which is drawn in at the axis of the turbine pump, to the scroll for connection to a user device.
The number of vanes of each impeller and their geometric and structural configuration depend on hydraulics and physics relations which are well-known and used by designers.
Twisting vanes, i.e., vanes of the double-curvature type, are frequently employed.
These impellers are currently obtained by introducing the molten metal, generally cast iron, in a die preset for this purpose, which in practice constitutes the complementary pattern from which the impellers take their shape. shape.
The die being used bears the impressions of the two disk-shaped elements and internally comprises a core suitable to shape the impressions of the fluid conveyance vanes.
The core is generally made of pressed and baked sand, is substantially toroidal and acts as a die body for the vanes.
In practical execution, it is necessary to start from the drawing of a theoretical design vane produced by a designer.
A modeler must then reproduce said theoretical vane in a real prototype, which is shown schematically in FIGS. 1 and 2 and designated by the reference letter A.
Once the modeler has created the vane prototype A, such prototype is used to form the pressed and baked sand core, designated by the reference letter B in the above figures.
Once the core B has been formed, production of the impeller continues by inserting the core in the die and by introducing the molten metal.
Moreover, the vane prototype A can currently be extracted from the core B only through the combination of a double movement which includes an outward translatory motion and a simultaneous lifting of the prototype, as shown schematically in FIGS. 1 and 2 by the arrows C and D.
The prototypes A of the vanes, by which the core B is shaped and which are obtained from a theoretical drawing, have a twisted shape; this causes great difficulty in production of vanes requires planing, filing, modifications and retouches of the structures of all the prototypes A.
In other words, the modeler has to retouch the first time each prototype A, performing a plurality of operations that remove material until the prototype can be extracted from the sand core B without risking damage to the core.
At the end of the adjustments, turbine pump impellers are obtained whose vanes have shapes which do not match the hydraulic theoretical models and which, in practical applications, reduce the hydraulic efficiency of the turbine machines.
The process for modifying and adapting the prototype A of each vane, in order to allow its easy extraction from the sand core B, usually requires a long time (which in any case cannot be estimated in advance) and entails significantly high costs, consequently constituting a burden for the first step of production.
Sometimes the modeler is forced to intervene more than once, starting each time from the very beginning, because he makes mistakes in planing and modifying the structure of the prototype A.